The debranning of common wheat : an innovative tool to improve flour characteristics

Debranning removes the external layers of kernels by means of abrasive action. This pre-milling operation is necessary in the case of covered cereals (as rice, oats, barley) in order to remove hulls with no technological and nutritional interests. Debranning is less frequent in the “naked” (hull-less) grain processing. In the present study the effects of this operation were examined on common wheat: above all we considered the possibility of increasing the yield and improving the hygienic characteristics of flour. The removal of a part of bran before milling, in fact, can reduce the risk associated with mycotoxins, contaminants present in the outer regions of kernels. The research was carried out by a pilot-plant debranning machine, with innovative abrasive elements covered by synthetic diamond powder. The variables taken into consideration were the particle size of the abrasive elements, processing time, number of debranning steps and hydration conditions of kernels. The debranning effects were observed by Scanning Electron Microscopy and quantified by the evaluation both of the debranning level and several chemical and physical indices of kernels. The characteristics of debranning waste were compared with the bran obtained by the conventional milling process. In particular, the starch amount was considered as the “marker” of an excessive endosperm abrasion, negatively related to flour yield. The trials, carried on two types of common wheat (hard and soft), evidenced the importance of a preliminary hydration step to reduce kernel breakage. The best results were obtained with 3% of water, and hydration time less than 10 minutes. Synthetic diamond powder with fine particle size (180-200 mesh) allowed a uniform abrasive action, without deep grooves in the endosperm region. Debranning levels lower than 8-10% guaranteed low starch losses in the waste but, at the same time, noticeably reduced the microbial count of kernels. Removing a part of the bran shortened conditioning times before milling, up to 70%, compared to conventional process.